The long-term goal of this project is to develop a comprehensive knowledge of acute insulin signaling pathways. Much of insulin signaling proceeds by changes in the extent of phosphorylation on specific sites of proteins. The majority of these sites and the effects of their changes in phosphorylation are still unknown. We refer to all the sites in the cell that undergo changes in phosphorylation in response to acute insulin treatment as the insulin phosphoproteome. The advent of new technologies in phosphopeptide isolation and mass spectrometry now enable the comprehensive determination of the insulin phosphoproteome. Identification of a site on a protein that changes in phosphorylation in response to insulin is the first step in elucidating the functional role of the phosphorylation change in insulin action. We propose one very substantial specific aim. We will determine and analyze the insulin phosphoproteome in cultured adipocytes, myotubes, and hepatocyte-like cells. These are models for the three main target tissues of insulin action: fat, muscle and liver. Through the use of specific kinase inhibitors we will assess where each site of insulin-regulated phosphorylation is located within the currently known framework of insulin signaling. This proposed research is most directly relevant to type 2 diabetes, a disease that afflicts about 20 million Americans. A key component of type 2 diabetes is insulin resistance, the state in which cells exhibit reduced responsiveness to normal levels of insulin. The proposed research will lead to a more complete understanding of insulin signaling and action. This knowledge is a necessary basis for understanding of the changes that occur in the insulin-resistant state of type 2 diabetes.